Brazing and solder compositions comprising a chelating agent

ABSTRACT

IMPROVED BRAZING OR SOLDERING PASTE COMPOSITIONS COMPRISING A METALLIFEROUS OR BRAXING SOLDER POWER AND A FUGITIVE RESINOUS BINDER HAVE BEEN DEVELOPED. THE IMPROVEMENT COMPRISES A CHELTING AGENT DISPERSED THEREIN IN A PROPORTION OF ABOUT O.3-10% BY WEIGHT OF THE BINDER, THE CHELTING AGENT BEING SELECTED FROM THE GROUP CONSISTING OF TETRAKIS HYDROXYALKYL DERIVATIVES OF ALKYLENE DIAMINES, TETRAKIS CARBOXY ALKYL DERIVATIVES OF DIAMINE, ALKALI METAL SALTS OF TETRAKIS CARBOXY ALKYL DERIVATIVES OF ALKYL DIAMINES AND HYDROXY CARBOXYLIC ACIDS.

United States Patent 3,832,242 BRAZING AND SOLDER COMPOSITIONSCOMPRISING A CHELATING AGENT Stanley G. Cuthbert, Munster, Ind.,assignor to SCM Corporation, Cleveland, Ohio No Drawing.Continuation-impart of abandoned application Ser. No. 57,822, July 23,1970. This application Aug. 17, 1972, Ser. No. 281,543

Int. Cl. B23k 35/34 U.S. Cl. 148-24 Claims ABSTRACT OF THE DISCLOSUREImproved brazing or soldering paste compositions comprising ametalliferous or brazing solder powder and a fugitive resinous binderhave been developed. The improvement comprises a chelating agentdispersed therein in a proportion of about 0.310% by weight of thebinder, the chelating agent being selected from the group consisting oftetrakis hydroxyalkyl derivatives of alkylene diamines, tetrakis carboxyalkyl derivatives of diamine, alkali metal salts of tetrakis carboxyalkyl derivatives of alkyl diamines and hydroxy carboxylic acids.

This application is a continuation-in-part of my application having Ser.No. 27,822 (Series of 1970) and having a cfiling date of July 23, 1970,now abandoned. All information set forth in that case is herebyincorporated by reference.

Brazing and solder compositions in the semi-fluent state, e.g., pastes,for metal working have been widely used where the shaped solid metalslugs, foils, strips, etc., have been difficult to use in such brazingand soldering operations. One of the major problems encountered with theuse of such brazing or soldering compositions in semifluent form hasbeen the tendency of the suspended metalliferous powder to settle outprior to application. As a result, it became very difiicult to apply apredetermined quantity of the metalliferous powder to the joint, therebynecessitating the reblending of the brazing composition prior toapplication.

There is an abundance of information written about the brazing andsoldering art as such art has been in use for centuries. Descriptions ofbrazing and soldering equipment used for carrying out the brazing andsoldering operations as well as metals which can be brazed or solderedhave also been reported. Furthermore, brazing and soldering fillermaterials, i.e., the compositions of metals, metal alloys used as afiller material in brazing and soldering, are also described in theliterature. Texts particularly good in describing the state of the artare Kirk and Othmer Encyclopedia, Volume 18, pages 541 through 548published by McGraw-Hill in 1971; the book entitled Brazing Manual,published by the American Welding Society 1963; Specification forBrazing Filler Metal published by the American Welding Society in 1969and the Welding and Brazing section of the Metals Handbook, 8th edition,volume 6, published by the American Society for Metals in 1971. Suchinformation relating to brazing and solder filler metals used forbrazing is incorporated by reference.

Advantages of the compositions set forth herein for metal-workinginclude: excellent stability of the semifluent composition andmetalliferous powder therein; excellent flow control of the semi-fluentcomposition for extruding, spraying or otherwise applying thecomposition to the workpiece; excellent adherence of the composition onapplication to the workpiece; and substantially uniform dosages ofpowder to the workpiece.

An improved brazing or soldering paste composition comprising ametalliferous brazing or solder powder and a fugitive resinous binder isprovided with the improvement comprising a chelating agent dispersed insaid brazing or soldering paste composition in a proportion of fromabout 03-10% by weight of the binder, said chelating agent selected fromthe group consisting of tetrakis hydroxyalkyl derivatives of alkylenediamines, tetrakis carboxy alkyl derivatives of diamines alkali metalsalts of tetrakis carboxy alkyl derivatives of alkyl diamines, andhydroxy carboxylic acids.

In brazing alloys (and silver soldering alloys), the principalconstituents usually are copper, silver, nickel, cadmium, and/or zinc.Sometimes, it is advantageous to use copper alone as a brazing alloy orcopper dosed with minute proportions of phosphorous, silicon, manganese,or aluminum. Also, other minor constituents for alloying use generallyinclude gold, indium, boron, bismuth, antimony, chromium, titanium, andlead. When the brazing or silver soldering of a joint is practiced in areducing atmosphere, the oxides of metals reducible under thoseconditions to the elemental metal can be used (e.g., oxides of thenonrefractory type) such as copper oxide, silver oxide, nickel oxide,zinc oxide, and the like.

Particularly desirable brazing compositions which have been well suitedfor the practice of the present invention are those employing a copperbase for brazing at a temperature of from 1300-2100 F. and thoseemploying a nickel base for brazing at temperatures from 1900-2400 F.Copper alloy brazing compositions as a filler metal for making brazingpowders are found on page 548 in the Kirk and Othmer Encyclopedia citedhereinbefore. Pages 152 through and pages -205 of the cited BrazingManual by the American Welding Society describe the nickel base systems.Further compositions of copper and nickel brazing alloys are found inthe Brazing and Welding Handbook by the Metal Society. All brazingcompositions cited in each of these references are incorporated byreference as being exemplary of the brazing compositions suitable forpracticing the invention. Silver, gold, and palladium brazing soldercombinations are also reported in these references and can be used, butare quite expensive and, therefore used in selected applications. Forreasons of efliciency and economy, the copper and brass powder alloysthereof, and the nickel base alloys for brazing purposes are thepreferred metalliferous powders used in the formulation of the brazingcompositions.

For reasons of clarity, the term metalliferous powders is meant to referto those brazing or solder alloys compositions conventionally used inthe brazing or soldering art as cited herein.

The metalliferous alloys materials are comminuted to a fine particulateform (powder) so that they are easily dispersed in the fugitive binderand maintained in suspension. Additionally, such comminution oftenprovides for quicker melting and better flow of the metalliferous powderinto the joint at the brazing temperature. The metalliferous powdertypically is finer than 100 mesh U.S. Standard Sieve as larger particlesare difiicult to disperse and maintain uniform in the paste. Metalpowders having a particle size of 325 mesh U.S. Standard Sieve, andfiner, are employed generally and are quite satisfactory for making thecompositions of the present invention. However, the use of metal powdershaving particles finer than 325 mesh U.S. Standard Sieve often does notresult in cor- }.responding improvement in the suspendability of themetalliferous powder or stability of the composition.

Fugitive binders containing resin have been employed in preparingbrazing and soldering compositions and are widely used for facilitatingthe adhesion of metal powder to the metal substrate to be worked, e.g.,brazed, soldered, filled, etc. These fugitive binders are typified byhaving a low Conradson value below about 1% so that very little, if any,carbonaceous material remains as a residue after metal-working which mayinterfere with the strength or appearance of the worked part. TheConradson test is described in ASTM Standards D-l89-46, Part III-A, page120 (1946) and is also referenced in US. Pat. 2,566,339.

The binders are fugitive in that they decompose at the workingtemperature of the heated zone and preferably much lower, e.g., 400550F. The fugitive binders on decomposing, form volatile compounds whicheither burn or pass off as gaseous material. Any residue might interferewith the strength of the joint, etc. resulting from Working. Thefugitive binder should also be smokeless and odorless at the temperatureof the heated zone so that it will not interfere with the operation.Additionally, the fugitive binders should be quicksetting on applicationto prevent the metalliferous powder from blowing away or rubbing offprior to heating in the heated zone. Typically, these resins set by airhardening and form a film. Air hardening may be simply volatilizing ofsolvent resulting in coalescence of the binder particles.

Resins for making up the fugitive binders having the above propertiesand conventionally used in preparing razing and solder compositions arehomopolymers and copolymers of the lower alkyl esters of acrylic andmethacrylic acid (those having from 1-8 carbon atoms), e.g.,methylmethacrylate, ethylacrylate, methylacrylate, 2-ethyl hexylacrylate, or mixtures thereof, polystyrene, polyvinyl chloride,polyvinyl acetate, butadienestyrene latices, polytetrafiuoroethylene,cellulosic polymers, e.g., cellulose acetate, cellulose nitrate,cellulose acetate butyrate, etc., polyolefins, e.g., polypropylene,polyethylene, epoxy resins, polyesters, rosin, e.g., tall oil rosin, gumrosin, etc. For eificiency and economy, the lower alkyl esters (C -C ofacrylic and methacrylic acid are preferred. The resin is used primarilyto hold the metalliferous powder on the workpiece prior to actualworking. Sufficient resin is used to accomplish such holding which isusually from about 15-60% resin by weight of fugitive binder. Becausethe resin is burned away during brazing, welding, etc. the amount ofresin used is kept at a minimum where possible to reduce costs.

Chelating agents sometimes referred to as complexing agents or ligandsfor complexing metals of the type used herein are widely known and canbe used in practicing this invention.

The chelating agents useful for practicing this invention comprisetetrakis hydroxy alkyl derivatives of alkylene diamines, tetrakiscarboxy derivatives of alkylene diamines, alkali metal salts of tetrakiscarboxy alkyl derivatives of alkylene diamines, and hydroxy carboxylicacids. Generally, the alkali metal salts of the tetrakis carboxy alkylderivatives of alkylene diamines leave a residue, believed to be causedby the alkali metal in the salt. These salts are not used often becauseof this deleterious affect on the joint. The other totally organicchelating agents do not leave a residue and are preferred. Sequester ingagents differ from the chelating agents in that the sequestering agentreacts with the metal ion to produce a soluble complex. But, forpurposes of this invention, the term chelating agent includessequestering agents.

Virtually any type of chelating agent, optionally dispersed in water orsolvent, can be used in this invention. The chelating agent should beone that on heating to the brazing or soldering temperature does notleave a substantial carbonaceous or metal ash of more than 0.5% byweight as measured by the Conradson test and does not produce anoffensive odor or smoke.

A minor proportion of chelating agent relative to the portion of resinin the binder is used for enhancing the stability of the suspensionformed on dispersing the metalliferous powder in the fugitive binder.Generally an effec tive proportion of chelating agent between about03-10% by weight of the fugitive binder, and preferably between about0.52% is employed.

Organic chelating agents as opposed to inorganic chelating agents areparticularly adapted for use in preparing the brazing and soldercompositions because they leave relatively small amounts of ash, if any,as residue and burn away during the brazing or solder operation.Inorganic chelating agents often leave a slight amount of metal ashafter metal-working in the heated zone and the metal compound may not becompatible with the metalliferous powder or workpiece.

The tetrakis carboxy alkyl derivatives of alkylene diamines and alkalimetal salts often are referred to as amino polycarboxylic acid andalkali metal salts thereof. Examples of this chelating agent includeethylene diamine tetracitric acid, N-hydroxyethyl (N ,N ,N-ethylethylene diamine triacetic acid) and the alkali metal saltsthereof.

The tetrakis hydroxy alkyl derivatives of alkylene diamine include N,N,N,N -tetrakis 2-hydroxypropylethylene diamine, N, N, N N -tetrakis,Z-hydroxypropyl propylene diamine, and so forth. Hydroxy carboxylicacids are known as being elfective chelating agents and these are thetype referred to here. They generally have from 3-6 carbon atoms in thestructure such as tartaric, lactic, gluconic, citric, and hydroxy aceticacid. Other conventional chelating agents such as the amino alcohols,e.g., diethanol amine and triethanol amine, hydroxy-[S-diketones, e.g.,acetyl acetonate, which provide minor chelation when mixed with brazingor soldering paste compositions, do not impart the stability that thestronger chelating agents set forth above impart to the brazing andsoldering paste compositions. Stability of only a few days is noted withthe weaker and conventional chelating agents, whereas the chelatingagents described herein impart stabilities of several weeks to months.It is believed that enhanced stability of the dispersion is primarilydue to firstly, the chelating action of the agent, i.e., tying up themetalliferous powder, and secondly, the reaction of the chelating agentwith the resin to form a thickened mixture.

Optionally, solvents can be used where desired for dissolving the resinsand to place the fugitive binder composition in a form suitable forapplication. The solvent should volatilize readily at temperatures ofabout 300 F. and decompose without producing substantial amount ofcarbonaceous residue, smoke or odor during a brazing operation.Additionally, the solvent should be relatively non-volatile of about 70F. and atmospheric pressure. If the solvent is too volatile, thefugitive binder will have a tendency to dry out without resultingadhesion and the metalliferous powder and fugitive binder may blow awayprior to brazing. Advantageously, hydrocarbons such as hexane, heptane,kerosene, pentane, aromatic solvents such as benzene, naphthas toluenehaving a boiling point of up to 450 at atmospheric pressures, ketonesolvents such as acetone, methylisobutyl ketone, methyl ethyl ketone,isobutyl ketone, and the like, glycols, such as ethylene, propylene, anddiethylene glycol, esters such as methyl acetate, ethyl acetate, butylacetate, monoethyl ether acetate, and the like, alcohols such asethanol, propanol, methanol, ether alcohols such as Z-ethoxy ethanol,2-ethoxy butanol, and ether ketones such as 4-methoxy-4-methyl-pentanone-2-, and the like can be employed. Water can also beused as a solvent. However, water is often objectionable because thecomposition spatters in the heated zone.

In formulating the fugitive binder, various proportions of solvents canbe used in dissolving the resin and dispersing the metalliferous powderfor achieving desired composition viscosities. Composition viscosities,for example, can range from 3,000 to over 100,000 centipoises at 75 F.Compositions having lower viscosities normally are used for applicationsby spray or brush techniques. Compositions having higher viscosities areemployed when the material is spread with a doctor blade, putty knife,etc. Generally, the fugitive binder contains from 50-90% solvent byweight and preferably about 80% to give a 20% solids content.

Optionally fluxes can be used as an additive to the brazing or soldercompositions where desirable. Virtually any of the fluxes used in suchbrazing or soldering compositions can be employed here and examples ofsuch fluxes include alkali metal fluoroborates, alkali metal carbonates,alkali metal tetraborates, boric acid, and hydrohalide salts ofhydroxyamines such as 2-amino-2-methyl-1,3-propanediol. Preferably notmore than of such fluxing agent by weight of the composition is used.

Th materials adapted for working with this composition primarily are theferrous-containing materials, e.g., iron, cast iron, steel, e.g.,stainless, mild, low and high carbon, etc., aluminum, brass, alloys, andthe like. The compositions can be used for conventional metal-working,e.g., to fill voids, pits, and the like or used in forming a metal orporous metal film.

In working with the composition, it is applied to the part and allowedto set so that the composition will not blow away or rub off. The coatedpart then is introduced to a heated zone wherein the metalliferouspowder inthe composition fuses to metal flowing into the joint, pit,etc. The fugitive binder volatilizes at the zone temperature therebyleaving essentially metal and little, if any, carbonaceous or ashmaterial. The zone can be heated by a furnace as in furnace brazing,acetylene-oxygen torch, hot salt bath, electrical means, and otherconventionally used techniques in brazing or soldering.

The following examples are provided to illustrate preferred embodimentsof the invention but are not intended to limit the scope thereof. Allparts are parts by weight, all percentages are weight percentages, andall degrees are degrees Fahrenheit, unless otherwise specified.

EXAMPLE I A low viscosity brazing composition for spraying or dipoperation is prepared by charging to a vessel 2.2 parts of an aqueoussolution containing 30% of tetrasodium ethylenediamine tetraacetate,26.8 parts of 4-methoxy-4-methyl pentanone-2 and 11 parts of a solidparticulate polymer polymerized from a 50 part ethylacrylate: 50 partmethylmethacrylate mixture, having a specific gravity of 1.19 g./cc. andpencil hardness of H at 180 and 300. When 40 parts polymer are dissolvedin 60 parts toluene, the

viscosity of the resultant solution is between 400-700.

centipoises at 30 C. The charged materials are agitated until thecopolymer is dissolved to form a dispersion. Sixty parts of copperpowder passing through a 200 mesh U.S. Standard Sieve are added to thedispersion and then agitated until the copper powder is thoroughly mixedand suspended therein. The resultant dispersion on mixing thickens withapparent reaction between the chelating agent and resin and forms adispersion. The viscosity of the dispersion is 9,000 centipoises at 78F. The dispersion is extremely stable with very little copper powdersettling out over a period of 4 hours.

Steel workpieces to be joined are coated with the composition preparedabove at the joint of junction. On application, the composition sets upin about one minute. The workpieces then are passed into a furnace andheated to a temperature of 2050 F. for about 15 minutes in a reducingatmosphere until a substantially uniform temperature is reached, thencooled to room temperature (70 F.). The resulting brazed joint isextremely strong having substantially uniform amount of copper over thetotal area of the joint. No carbonaceous ash remains.

EXAMPLE II A high viscosity brazing composition is prepared in the samemanner as the brazing composition in Example I, except the chelatingagent is N,N,N ,N -tetrakis-2-hydroxypropyl ethylenediamine and 80 partscopper powder are used instead of 60 parts. The resultant compositionhas a viscosity of 120,000 centipoises at 75 F. and is extremely stablewith very little copper powder settling out over a period of severalweeks. Steel workpieces are joined with this brazing composition and theresulting joints are found to be extremely strong.

EXAMPLE III A brazing composition is prepared in the same manner as inExample I, except the chelating agent is titanium acetyl acetonate. Theresultant composition is extremely stable. A joint brazed with thiscomposition is strong, however, some of the titanium remains as metalash.

EXAMPLE IV A brazing composition is prepared in the same manner as thebrazing composition in Example II, except that the chelating agenttriethanolamine is used. The level of triethanolamine employed remainsthe same as the chelating agent in Example H. The resultant compositionbehaved like Newtonian fluid and settling began almost immediately. Atthe end of a three-day period, the powder had settled out hard and couldnot be redispersed.

EXAMPLE V A brazing composition is prepared in the same manner as thebrazing composition in Example II, except the filler metal is a nickelbase alloy, whose nominal composition is 14% Cr; 3% B; 4% Si; 4% Fe;0.7% C; and the balance Ni. The resultant composition is extremelystable with little settling over a period of several weeks. A stainlesssteel workpiece was joined utilizing the above brazing composition at2100 F. under a protective atmosphere of dry hydrogen. The resultingjoint was extremely strong.

What is claimed is:

1. In a brazing or soldering composition wherein a metalliferous powderis dispersed in a fugitive binder, the mprovement which comprises achelating agent dispersed in said binder in a proportion of about 03-10%by weight of the binder for maintaining said powder suspended therein,said agent is selected from the group consisting of tetrakishydroxyalkylderivatives of alkylene diamines, tetrakiscarboxyalkyl derivatives ofdiamines, alkali metal salts of tetrakiscarboxylalkyl derivatives ofalkylene diamlnes, and hydroxycarboxylic acids, said powder having aparticle size between 100 and 325 Mesh (U.S. Std. Sieve Series) andbeing present in a proportion of from about 55 to by weight of thecomposition, while said binder being present from about 25 to 40% byweight of the composition, and said binder comprising by weight fromabout 10 to 50% of a resinous material having a Conradson carbon valueof about 1% and from about 50 to of an organic solvent.

2. The composition of Claim 1 wherein said metalliferous powder iscopper or copper oxide.

3. The composition of Claim 1 wherein said metalliferous powder isbrass.

4. The composition of Claim 1 wherein said metalliferous powder isnickel or alloys thereof.

5. The composition of Claim 1 wherein said chelating agent is N,N,N ,N-tetrakis-Z-hydroxypropyl ethylene diamine.

6. The composition of Claim 1 wherein said chelating agent istetrasodium ethylenediamine tetraacetate.

7. The composition of Claim 1 wherein said resinous Int 13611211 is apolymerized ester of acrylic or methacrylic aci 8. The composition ofClaim 1 which further includes a fluxing agent not substantially morethan 10% by weight.

9. The composition of Claim 8 wherein said fluxing agent is selectedfrom the group consisting of alkali metal fluoroborates, alkali metalcarbonates, alkali metal tetraborates, boric acid, and hydrohalide saltsof hydroxyamines.

10. The composition of Claim 9 wherein said fiuxing agent is2-amino-2-methyl-1,3-propanediol.

References Cited UNITED STATES PATENTS Neilson 148-25 Noble et a1148-126 Evans et al. 148-24 Klinker 148-25 Linnert et a1 117-132 Mueller106-48 X Lindquist 106-39 R Williams 148-25 Forker 148-25 Brightly148-23 Arorrberg 148-26 Miller 148-25 Melchiors et a1 148-25 3,272,8619/1966 Riggs 148-25 3,589,932 6/1971 Burne 148-24 3,575,738 4/1971Becker 148-25 OTHER REFERENCES Martell, A.; Chelation, in Chemistry ofMetal Chelates Compounds; New York, 1952, pp. 9-15.

Dwyer, F.; Bidentate Chelates, in Chelating Agents And Metal Chelates;New York, 1964, pp. 95-97.

Chaberer, 8.; Types of Metal Chelale Compounds; in Organic SequesteringAgents; New York, 1959, pp. 69.

Heslop, R., et al.; Inorganic Chemistry; New York. 1967, pp. 565-9,586-95 and 599-601.

1 WALTER R. SATTERFIELD, Primary Examiner US. Cl. X.R. 148-23, 25, 26

UNITED STATES PATENT ()FFKIE CE'HFICATE OF CORRECTION PATENT NO.3,832,242

DATED August 27, 1974 INVENTOR(S) Stanley G. Cuthbert It is certifiedthat error appears in the ahoveidentified patent and that said LettersPatent are hereby corrected as shown below:

Column 3, Column 3, Claim 10, line 2,

[SEAL] line 48, line 48,

Signed and Scaled this fif ay of August1975 Arrest:

RUTH C. MASON Arresting Officer C. MARSHALL DANN ('ummr'ssr'mrcrnj'lalents and Trademarks

